Acid treatment of thionaphthene vat dyestuffs



Patented July 12, 1949 UNITED STATES PATENT OFFICE ACID TREATMENT OF THIONAPHTHENE VAT DYESTUFFS John F. Cullinan and Lawrence D. Lytle, Plainfield, N. J., assignors to American Cyanamid Company, New York, N. Y., a. corporation of Maine No Drawing. Application March 13, 1944, Serial No. 526,344

Claims.

This invention relates to an improved process of transforming vat colors into a form having a very fine and substantially uniform particle size.

More particularly the present invention relates to an improved process whereby dyestuffs in the desired uniform, finely-divided state are obtained from indigoid vat dyestuffs characterized by the presence of at least one thionaphthene nucleus. Typical examples of the dyestuffs in this group may be represented by the following:

k ll=C2' Acenaphthene (1)-thionaphthene (2) indigo (C. I. 1228) Of particular importance in this series are the dyestuffs of the thioindigo type such as, for example,

6,6-diethoxy-thioindigo (C. I. 1217) III Bis-4,5,4 ,5-benzothionaphthene- (2,2 -indigo on, f CH 4,4-dimethyl-6,6-dichloro thioindigo V O tained as coarse crystalline materials or as relatively large agglomerated particles. In this state, they are unsuitable for use in printing, pigment dyeing, emulsion printing and the like operations. As a consequence, various procedures have been proposed to reduce their particle-size and thereby improve their penetrating ability and reactivity.

Commercially, the most common of these processes comprises the steps of dissolving the pigment in concentrated sulfuric acid and reprecipitating it by dilution with water, usually by drowning the entire solution in a large excess of water. Modifications have been proposed in which the dilution is carried out in other ways. Those have included, for example, addition of dilute sulfuric acid in a quantity only sufficient to precipitate a sulfate which can be collected and hydrolysed; or accomplishing the dilution with water of crystallization by using such hydrated materials as Glaubers salt and the like. The effect of varying the operating temperatures has also been proposed as a means of control.

These processes have been of little value when applied to thioindigo dystuifs. These dyestuffs were difiicult to obtain in fine particle sizes and the importance of uniformity and its necessary relation to fineness was not properly considered. In general, therefore, thioindigos as prepared according to the teachings of the prior art lacked suflicient uniformity of particle size and contained larger particles in addition to the small ones. As a result, there remained a demand for a method adapted to produce a more finely divided color or more uniform size.

It is, therefore, a principal object of the present invention to develop such a process, capable of producing particles having the desirable properties of fineness and uniformity of particle size. In general, the desired object is accomplished through an improved process of carrying out the treatment of the materials with sulfuric acid.

According to the present invention, it has been found that in the treatment with sulfuric acid, there is for each material a specific range of acid concentrations which produce the optimum result. In addition, it has been found that the proportions between the dissolved and undissolved material at any stage in the process is of equal, if not greater importance. This involves not only the acid concentration, but also the total amount of acid present. Variations also result from changing the temperature at which the reaction is carried out, the procedure by which the correct acid concentration is reached and to a lesser extent with the time of contact. All must be reasonably controlled for the best results.

In developing the present process, the optimum acid concentration and amounts are such that only a very small quantity of dyestulf is dissolved and the dye is precipitated as its sulfate. It is necessary that the dyestuff have some solubility, otherwise it cannot be converted into a sulfate, and it is further necessary that at least one of its sulfates be slightly less soluble. It is the recognition and use of this differential solubility between the dyestuif and its sulfatewhich is responsible for the surprisingly improved results obtained by the process. The dyestuff, being slightly soluble, goes into a solution as such and is converted to its sulfate. But because the salt is less soluble, the solution becomes supersaturatedwith respect to the sulfate and the latter separates out.

It should be noted that at any given time the solution of the sulfate is exceedingly dilute. Consequently, the dissolved molecules are relatively far apart and their rate of aggregation in precipitating the insoluble sulfates is very low. At the. same time, because the concentration of sulfate remains essentially constant during the entire precipitation, the precipitated products, are not only very finely divided but have a 'very uniform size. Probably due to a pseudomorphosis, this fineness and uniformity is retained when they are subsequently hydrolysed with water, either with or without being previously isolated.

Expressed in general terms, therefore, the process of the-present invention comprises the treatment of indigoid vat dyestuffs characterized by the presence of at least one thionaphthene nucleus with the correct amount of sulfuric 'acid having the optimum concentration. At the same time, the proper degree of care is exercised in bringing the acid to the correct concentration before use and in maintaining a substantially uniform temperature throughout the process.

According to the above considerations, the principal factors to be controlledar'e: (1) the acid concentration; (2) the amount of acid; (3) the temperature; and (4) the-mannerof reaching the optimum acid'concentration. Each of these has a direct bearing on the treatment of any particular dyestuff. Consequently, each factor is subject to certain limitations.

As far as the .acid concentration is concerned, the individual .dyestufis vary widely in their .optimum acid ranges. For any particular dyestufi the exact acid range most suitable thereto can not be assigned numericallimitationswhich will in turn be applicable to all cases. Functionally, a more exact limitation can be assigned in terms of solubility. The lower limit is that acid concentration at which the specific dyestuff has a slight solubility. The upper limit is that concentration at which a sulfate ofv dyestuff has only a very limited solubility so as to form readily a supersaturated solution of the sulfate.

In treating the thionaphthenedyestuffs of the present invention, it is important that the sulfuric acid be diluted to the proper concentration before being used. If the dyestuif is dissolved first in concentrated acid and the resultantsolution is then diluted to the proper strength, the desirable result is not obtained. In some cases the dyestuff itself is sulfonated by the concentrated acid. In other cases only a-coarse material is obtained because precipitation by diluting a rather concentrated solution favors the formation of large particles. Itis-desirable, therefore,

to have the initial concentration as low as is practically possible.

So far as the amount of acid used is concerned, at least of the solid products should remain undissolved at any point in the process. Preferably, the undissolved material should be as great as practically possible so the 98%, or more, remains undissolved. Because the amount of undissolved material present during the process is an important consideration, there is obviously an inter-relation between the acid concentration and "he amount of acid used. The latter, however, is not as critical as the former. As pointed out above, the'amount of acid used may vary. To a certain extent this is limited by practical considerations. Obviously, an insufficient amount of acid produces a very thick, unstirrable slurry. On the other hand, too great an amount of acid is impractical because of the volume required and the consequent decrease in the productive capacity of the equipment. At the same time, too great an amount of acid will dissolve excessive amounts of the dyestufi and sulfate. As-was indicated above, this is undesirable if the optimum fineness and uniformity of particle size is to be obtained.

For all practical purposes, the amount of acid used will be found to be about 10 to 40 parts per part of dyestuff. However, in all but extreme cases, these limits can be considerably narrowed. It is usually found that good results will be obtained using between about 20 to 30 parts of acid per part of dyestuff. Because of the relation to the acid concentration, the amount in some cases may require adjustment with respect thereto.

Because in effect, it is the solubilities of the various materials which it is necessary to control, the problem of temperature cannot be overlooked. Marked changes in temperature will alter the solubilityof materials in any designated strength of acid. Therefore the temperature of the reaction should not be allowed to vary sufficiently to appreciably affect the solubility during the course of the reaction. It is .most convenient to work at approximately room temperature. Consequently, the experimental data taken in developing the present invention is based on tem peratures of about 25-35 C. However, should it become desirable to operate at higher or lower temperatures, an adjustment in either or both the strength and amount of acid to compensate therefore can be readily made in accordance with the solubility limitations set forth above.

The time cycle should also be considered. Obviously, if the time of contact is too short, all of the pigment will not be converted into finelydivided sulfate. On the other hand, if the time of contact is unduly prolonged, particles of precipitated sulfate will gradually grow because of the known tendency of crystals to increase in siZe when maintained in contact with a saturated solution of the mother liquor. There is some inter-relation between the time cycle and the acid concentration. However, in the instant invention, this is relatively unimportant since the range of optimum acid concentrations is so close that the time cycle varies but little between the upper and lower limits.

After conversion to the finely-divided sulfate is complete, the dyestuif must be hydrolysed. This may be done whether before or after isolation. A good general practice is to drown the slurry in about 4 to 8 times its volume of water. The precipitated product may'then be isolated after-dilutingthe solution to a convenient acid strength for practical filtration. Subsequently the dyestufi is usually washed on the filter until neutral. Preferably, but not necessarily, this washed filter cake is subjected to further treatment with a suitable deflocculating agent.

As an indication of the efiiciency of the process, the following test has been found particularly useful. About 100-200 mg. of dispersed dyestufi" is suspended in 200 ml. of distilled water at about 50 C. and approximately one-half of this suspension is poured on a three inch conical, glass filter funnel fitted with a dry No. 1 Whatman filter paper. The suspension is allowed to filter by gravity. If the dyestufi is finely divided and uniformly dispersed, most of it should go through the filter into the filtrate, and the residue on the paper should be small.

Test dyeings are then carried out, using the filtrate and the unfiltered portion of the suspension, the strengths of the resultant dyeings being compared. The filtrate of a well-dispersed product gives a dyeing having about 75-90% the strength of the unfiltered product. It is readily apparent that the greatest dye strength from the filtrate is obtained only when the procedure of the present invention has been carried out so as to produce a maximum of finely divided particles of uniform size.

It is surprising, and entirely unexpected, that the use of more concentrated acids than are indicated by the limits of the present process, but still not sufficiently high to promote sulfonation, produces a great amount of coarser particles as shown by the filtration test. Probably it is due to the fact that the higher strengths of acids have too great a solvent action on the dyestuff. As a result the soluble molecules are closer together and have a greater chance to precipitate as larger particles of the sulfate. Obviously also. still more concentrated acid will dissolve substantially the dyestuff, so that the sulfate will be precipitated only after dilution or it will sulfonate.

Thus the principal advantages of the present invention lie in its ability to produce very small particles of uniform size. This uniformity of small particle size is of great importance, for example, in a pigment padding process. In such a process, fineness is essential to good penetration but if the particle size is not uniformly small, the coarser particles do not penetrate to the same extent as the finer material and uneven dyeings result. Similarly, in printing vat dyestuffs a fine product size is important in order that reduction may take place quickly but if uniformity is lacking the resultant print is not properly level.

The invention will be more fully illustrated in connection with the following examples in which all parts are by weight unless otherwise noted.

Example 1 One part by weight of the scarlet dyestuif of the Formula I was treated with parts by weight of varied concentrations of sulfuric acid for 1'7 hours. The optimum acid strength to get a uniform particle size was 83.5%. The filtration test showed that the filtrate had 80% of the dyeing strength of the unfiltered product. Slightly lower or slightly higher acid strengths, such as 80% or 85.7% gave products of considerably poorer filtration test, in both cases the filtrate having only 50% of the dyeing strength of the unfiltered product. At an acid concentration of 88.9%, the dyeing strength of the test filtrate was only 40%. The precipitated sulfate of the dyestuff is of scarlet color.

Ewample 2 When the dyestuif of Example 1 is processed by dissolving it first in concentrated sulfuric acid and diluting the solution afterwards so as to obtain a slurry in the same amount of sulfuric acid of the same concentration as corresponds to the optimum conditions of Example 1, a product of greatly inferior dispersion is obtained. After the slurry has been stirred for 18 hours the product gave a filtration test in which the filtrate showed only 30% of the dyeing strength of the unfiltered product.

Example 3 One part by Weight of the orange dyestuff of the Formula II is treated with 25 parts by weight of sulfuric acid for 18 hours. The optimum acid strength is 93%. In this case the filtration test showed that the filtrate had 90% of the dyeing strength of the unfiltered product. At lower acid strengths of 87 or 91% the dyeing strengths of the filtrates were only 75 and respectively. If the acid is stronger, for example 95%, sulfonation occurs. The precipitated sulfate of the dyestufi is black.

Example 4 One part by weight of the brown vat dyestuif of the Formula III was treated with 25 parts by weight of the sulfuric acid for 17 hours. The optimum acid strength was 93.7% in which case the filtration test showed that the filtrate gave 75% of the dyeing strength of the unfiltered product. At a slightly lower acid strength of 92.5% the dyeing strength of the test filtrate was only 7 0% and when acid concentrations of 89% and of 96% were used, the dyeing strength of the test filtrates was very poor. The precipitated sulfate of the dyestuff is brown.

Example 5 One part by weight of the pink dyestuff having the Formula IV is best treated with 25 parts of an acid of the strength 98%. In this case the filtration test showed that the filtrate had a dyeing strength of 80% of the unfiltered product. It is necessary to keep this concentration; 100% sulfuric acid causes sulfonation while on the other side 95% sulfuric acid gave a product, the filtration test of which showed that the filtrate had only 70% of the dyeing strength of the unfiltered product. The sulfate of the precipitated dyestuff is brown.

Example 6 One part by weight of the violet dyestuff expressed by Formula V was treated with 25 parts by weight of the sulfuric acid for 18 hours. The preferred acid strength is 98% in which case the filtration test gave a filtrate showing of the dyeing strength of the unfiltered product. The use of a acid or of a 99% acid gave products the filtration test of which showed that the filtrate had only 80% of the dyeing strength of the unfiltered product. The precipitated sulfate is a violet-black.

We claim:

1. The method of converting an indigoid vat dyestuff having at least one thionaphthene nucleus into very finely divided particles of substantially uniform size which comprises forming a slurry of the dyestufi" with 20-40 parts of sulfuric acid used in such concentration that at the reaction temperature at least a part, but not more than 10% of the total dyestuif is in solution at any one time, agitating this slurry until conversion of the dyestuff touthe substantially insoluble. sulfate is substantially complete, and hydrolyzing the sulfate to the dyestiifi.

2. A me'thodaccor'ding to, claim 1 in which-the amount andconcentrationrof acid used is sowbal- ,anced that not more than two .percent of the dyestuffis in solution atany time during the operation.

,3..?The method of converting anindigoid. vat

dyestufi comprising bis-4,5325 benzothionaph- .thene- (2,2') -indigo into very finely divided-particles of substantially uniform size whiohcomprises forming a slurry of the dyestuif with 20-30 parts of 93-95% sulfuric acid, agitating this slurry until conversion of the dyestuff to the substantially insoluble sulfate-is substantially complete,

and hydrolyzing the'sulfate to the dyestufi.

'4. The methocl of convertin an indigoid vat thioindigo intovery finely divided :particles of soluble sulfate is substantially .complete, .and hydr-olyzing the sulfate t 'the dyestufi.

, 5. 'I'heimethod of converting .an indigoid vat 5 97-99% sulfuric acid, agitating this slurry until conversion of the dyestuff to the substantially insoluble sulfate is substantially complete, and'hydrolyzing thesulfate to the-dyestufi.

JOHN F. CULLINAN.

LAWRENCE D. LYTLE.

REFERENCES CITED The following references-are of record in'the file of this patent:

UNITED STATES PATENTS Number Name Date 1,057,887 Schmidt et al. Apr. 1, 1913 1,145,934 'Steindorfi et al July 13, 1915 2,065,928 Wa-ldron Dec. 29, 1936 2 ,176,011 -Mur'ch et al. Oct. 10, 1939 2,284,685 Detrick et al June 2, 1942 FOREIGN PATENTS Number Country Date 9,269 Great'Britain 1914 9,975 Great Britain 1914 

